Identification of respiratory vagal feedback in awake normal subjects using pseudorandom unloading.

Evidence of the Hering-Breuer reflex has been found in humans during anesthesia and sleep but not during wakefulness. Cortical influences, present during wakefulness, may mask the effects of this reflex in awake humans. We hypothesized that, if lung volume were increased in awake subjects unaware of the stimulus, vagal feedback would modulate breathing on a breath-to-breath basis. To test this hypothesis, we employed proportional assist ventilation in a pseudorandom sequence to unload the respiratory system above and below the perceptual threshold in 17 normal subjects. Tidal volume, integrated respiratory muscle pressure per breath, and inspiratory time were recorded. Both sub- and suprathreshold stimulation evoked a significant increase in tidal volume and inspiratory flow rate, but a significant decrease in inspiratory time was present only during the application of a subthreshold stimulus. We conclude that vagal feedback modulates respiratory timing on a breath-by-breath basis in awake humans, as long as there is no awareness of the stimulus.     

The trajectory of a stiff rod in a curved potential energy trough

The equilibrium trajectory of the axis of a rod subject to an externally imposed curved potential energy trough tends to conform to the shape of the curved trough, but also tends to be straight because of elastic resistance to bending. The actual path of the axis is a balance between the two extremes. We consider a potential energy trough centered along a circular arc of radiusR. For a rod of small length compared toR, we show that the axis at equilibrium forms an arc of a circle of radius greater thanR. The value of the radius of the axial path depends on the relative values of the Hooke’s Law bending constant for the rod and the depth and width of the trough. Motivation for the calculation is provided by nucleosomal DNA, which conforms to the surface of a roughtly cylindrical histone core at physiological ionic strength, but is observed to unwind into a partially extended conformation at very low ionic strength. We suggest that the rigidity to bending of short DNA segments becomes sufficiently great at low ionic strength to overcome attractive interactions with the histone surface. Alternately, of course, if during the cell cycle mutually attractive forces between DNA and histone core are weakened at constant ionic strength, the same type of unfolding would be expected to occur as the strength of the DNA-histone contacts drops below the level required to overcome elastic resistance to bending of the DNA rod.     

Genomic complexity and plasticity of Burkholderia cepacia

Abstract Burkholderia cepacia has attracted attention because of its extraordinary degradative abilities and its potential as a pathogen for plants and for humans. This bacterium was formerly considered to belong to the genus Pseudomonas in the γ-subclass of the Proteobacteria , but recently has been assigned to the β-subclass based on rrn gene sequence analyses and other key phenotypic characteristics. The B. cepacia genome is comprised of multiple chromosomes and is rich in insertion sequences. These two features may have played a key role in the evolution of novel degradative functions and the unusual adaptability of this bacterium.     

Factor VIII: structure, function and analysis

Factor VIII is an important blood coagulation protein whose genetic deficiency leads to the serious bleeding disorder, classic haemophilia (haemophilia A).Here we review the structure, function and analysis of this protein for diagnostic and therapeutic applications. Because factor VIII is tightly associated with von Willebrand factor some recent work on the latter is also considered so as to clarify the relationship between them.     

A method for gene enrichment based on the avidin-biotin interaction. Application to the Drosophila ribosomal RNA genes.

A method of enriching, from the total DNA of an organism, for long DNA strands carrying a particular gene is described. The purified RNA corresponding to the gene is covalently attached to biotin via a cytochrome c bridge. This modified RNA is hybridized to the total DNA. Those DNA strands which hybridize are separated from all the other DNA, using the avidin-biotin interaction, by one of two methods. Avidin is covalently attached to submicroscopic polymer spheres; the complexes of avidin spheres with the DNA: RNA-biotin hybrids band in CsCl at a much lower buoyant density than does free DNA. Alternatively, the DNA:RNA-biotin hybrids are isolated by affinity chromatography on an avidin-solid support column. These methods have been used to prepare long single strands of Drosophila ribosomal DNA (rDNA) in high yield and 42 to 80% pure.     

On the application of polyelectrolyte limiting laws to the helix–coil transition of DNA. V. Ionic effects on renaturation kinetics

The bimolecular rate constant k₂ for the association of complementary polynucleotide strands has been observed to increase strongly with increasing ionic strength—in fact, proportional to its third or fourth power. This effect is here interpreted quantitatively by means of polyelectrolyte theory starting with the Wetmur–Davidson postulate of a pre-equilibrium between separated strands and aligned segments close to one another but unbonded. The correct form, a power dependence of k₂ on ionic strength, is predicted. Comparison of the theoretical exponent with data allows the conclusion that each of the two single-stranded segments in the aligned but unbonded configuration consists of about 13–16 nucletides (not to be confused with the much smaller number of bonded base pairs in the nucleus), and that this number, denoted by Q, is possibly correlated either with a minimum length for duplex stability or with the persistence length of a single polynucleotide strand. It is suggested that experimental determination of the dependence of Q on (G+C)-content may distinguish between these possibilities. It is also suggested that addition of sufficient amounts of divalent metal ions such as Mg²⁺, Ca²⁺, or Co²⁺ may reverse the dependence of k₂ on ionic strength; under these conditions, k₂ is predicted to decrease with about the first power of ionic strength. At fixed ionic strength, k₂ should increase with increasing concentration of divalent metal ion, and, in fact, the published observation that the formation of poly(A)·2 poly(U) from poly(A)·poly(U) and poly(U) is second order in Mg²⁺ concentration is here correctly predicted from a priori molecular considerations. Finally, published association rate data for oligonucleotides are discussed in the present theoretical context.     

A new method of in situ hybridization

A new method for gene mapping at the chromosome level using in situ hybridization and scanning electron microscopy is described and has been applied to mapping the rRNA genes of Drosophila melanogaster. Biotin is covalently attached to Drosophila rRNA via a cytochrome c bridge at a ratio of one cytochrome-biotin per 130 nucleotides by a chemical procedure. Polymethacrylate spheres with a diameter of ca. 60 nm are prepared by emulsion polymerization and are covalently attached to the protein avidin at a ratio of 5–20 avidins per sphere. The biotin-labeled rRNA is hybridized to denatured DNA in a chromosome squash. Upon incubation with a sphere solution, some of the biotin sites become labeled with spheres because of the strong non-covalent interaction between biotin and avidin. The chromosome squash is examined in the scanning electron microscope (SEM). Polymer spheres, which are visible in the SEM, are observed to label the nucleolus, where the rRNA genes are located.Contribution number 5121 from the Department of Chemistry.